Generally, the widely-used peripheral input device of a computer system includes for example a mouse device, a keyboard device, a trackball device, or the like. Via the keyboard device, the user may directly input characters and symbols into the computer. As a consequence, most users and most manufacturers of the input devices pay much attention to the keyboard devices.
Hereinafter, the structure and the function of a conventional keyboard device will be illustrated with reference to FIG. 1. FIG. 1 is a schematic top view illustrating the outward appearance of a conventional keyboard device. As shown in FIG. 1, plural keys 10 are installed on a surface of the conventional keyboard device 1. These keys 10 are classified into some types, e.g. ordinary keys, numeric keys and function keys. When one or more keys 10 are depressed by the user's fingers, a corresponding key signal is generated to the computer, and thus the computer executes a function corresponding to the depressed key or keys. For example, when an ordinary key is depressed, a corresponding English letter or symbol is inputted into the computer. When a numeric key is depressed, a corresponding number is inputted into the computer. In addition, the function keys (F1˜F12) can be programmed to provide various quick access functions.
Hereinafter, the components of a key structure of the conventional keyboard device will be illustrated with reference to FIG. 2. FIG. 2 is a schematic exploded view illustrating a key structure of a conventional keyboard device. As shown in FIG. 2, the key structure 2 comprises a keycap 21, a scissors-type connecting member 22, an elastic element 23, a membrane switch circuit 24, and a base plate 25. The membrane switch circuit 24 is disposed on the base plate 25. The elastic element 23 is arranged between the keycap 21 and the membrane switch circuit 24. The scissors-type connecting member 22 is arranged between the keycap 21 and the base plate 25. In addition, the scissors-type connecting member 22 is connected with the keycap 21 and the base plate 25. The scissors-type connecting member 22 comprises an inner frame 221 and an outer frame 222. The inner frame 221 has a rotating shaft 2211. The outer frame 222 has closed pivot holes 2221. After the rotating shaft 2211 is inserted into closed pivot holes 2221, the rotating shaft 2211 is pivotally coupled with the closed pivot holes 2221. Consequently, the inner frame 221 and the outer frame 222 are swingable relative to each other.
When the keycap 21 of the key structure 2 is in an initial state, the keycap 21 is at a first height (not shown). When the key structure 2 is depressed, the keycap 21 is moved downwardly in response to the depressing force. As the keycap 21 is moved downwardly, the inner frame 221 and the outer frame 222 of the scissors-type connecting member 22 are correspondingly swung such that the inner frame 221 and the outer frame 222 are in parallel with each other. While the keycap 21 is moved downwardly, the elastic element 23 is compressed by the keycap 21, and the membrane switch circuit 24 on the base plate 25 is pressed by the elastic element 23. Consequently, the membrane switch circuit 24 is triggered to generate a corresponding key signal. Meanwhile, the keycap 21 of the key structure 2 is at a second height (not shown). The difference between the first height and the second height indicates a travelling distance of the key structure 2.
When the key structure 2 is no longer depressed, the compressed elastic element 23 provides an elastic force to the keycap 21. In response to the elastic force, the keycap 21 is moved upwardly. As the keycap 21 is moved upwardly, the inner frame 221 and the outer frame 222 are towed by the keycap 21 and correspondingly swung. Consequently, the keycap 21 is returned to the first height.
That is, after the force exerted on the keycap 21 is eliminated, the keycap 21 has to be returned to the first height. For achieving this purpose, the elastic element 23 has to push the keycap 21 back to its original position. In addition, the inner frame 221 and the outer frame 222 need to cooperate with each other to precisely control the upward moving action of the keycap 21 in the vertical direction. In other words, the performance of the scissors-type connecting member 22 is a very important factor that influences the quality and the use life of the overall key structure 2.
Moreover, for combining the inner frame 221 with the outer frame 222, the user needs to manually prop open the outer frame 222 to widen the distance between the two closed pivot holes 2221, which are respectively located at bilateral sides of the outer frame 222. Consequently, the rotating shaft 2211 can be successfully inserted into the closed pivot holes 2221 to result in the combination between the inner frame 221 and the outer frame 222. The procedure of manually propping-open the outer frame 222 increases the assembling time of the key structure 2. Since procedure of propping-open the outer frame 222 cannot be automatically performed by a machine, the throughput is low.
For solving the above drawbacks, an improved scissors-type connecting member is disclosed in Taiwanese Utility Model Patent M448779. FIG. 3 is a schematic perspective view illustrating a scissors-type connecting member is disclosed in Taiwanese Utility Model Patent M448779. The structure of the scissors-type connecting member 22′ of FIG. 3 is similar to the structure of FIG. 2. In comparison with FIG. 2, the outer frame 222′ of the scissors-type connecting member 22′ has an entrance 2222. An entrance width L8 of the entrance 2222 corresponds to an axial length L9 of a rotating shaft 2211′ of the inner frame 221′. A guiding surface 2223 is arranged between a pivot hole 2221′ and the entrance 2222. For example, the entrance width L8 is equal to or slightly larger than the axial length L9 of the rotating shaft 2211′ of the inner frame 221′. During the process of combining the inner frame 221′ with the outer frame 222′, the rotating shaft 2211′ of the inner frame 221′ is introduced into the pivot hole 2221′ through the entrance 2222 at a specified angle and in a specified direction and moved along the guiding surface 2223. Moreover, the rotating shaft 2211′ of the inner frame 221′ has two flat slant surfaces 22111 and 22112. While the rotating shaft 2211′ is introduced into the pivot hole 2221′, the two flat slant surfaces 22111 and 22112 interfere with the bottom surface of the pivot hole 2221′ and the guiding surface 2223. Consequently, the rotating angle of the inner frame 221′ relative to the outer frame 222′ is limited.
Due to the design of the entrance 2222 and the guiding surface 2223, the inner frame 221′ can be combined with the outer frame 222′ quickly, and the scissors-type connecting member can be assembly automatically. However, if the assembled keyboard drops down (e.g., drops down accidentally or undergoes a reliability drop test before leaving the factory) or the assembled keyboard is hit by an external force, some problems occur. For example, the rotating shaft 2211′ of the inner frame 221′ is easily moved along the guiding surface 2223 and escaped from the entrance 222 at the specified angle and the specified direction. Under this circumstance, the scissors-type connecting member 22′ is disassembled and the components of the key structure 2 are scattered.
Therefore, the conventional key structure and the scissors-type connecting member need to be further improved.